I think the London Cast Recording sounds the way it does because it was recorded when Andrews was sick - I’ve never heard that it is a reflection in how she actually sang the role. If it was, I think it was a foolish discussion to plan the recording, regardless if you want to advertise the new sterio sound.
As the “generational” thing, I tend to agree, but it is also true that people don’t train their voices the way they used to. There is this odd view on here that being in a musical is automatically more difficult than doing a play, which is often wildly inaccurate. Hamlet and Lear are some of the most vocally taxing roles in the theatre, and that includes Evita. I would’t put Eliza’s vocal demands as particularly challenging for any trained singer, but she has to carry rather long scenes, and completely transform herself throughout the evening. It’s a challenging role, but not one that demands a regular alternate, providing the actress is trained. Unfortunately, even the more acclaimed actors of today are not vocally trainee in the way working actors need to be. The recent production Hamlet at the Public has to cancel several performances because the cast was losing their voice. I saw the production, and particularly Oscar Issac was screaming - and not in a healthful manner that was taking care of his voice - he was voluntarily straining and forcing his voice to produce “acting” moments. And that was a short limited run of two months!
So yeah, that’s why it’s such a big deal when big actors do “Long Day’s Journey” or “Iceman Cometh” the sheer amount of dialogue is challenging, not to mention the acting that goes with it. To produce a consistent performance that is vocally and emotionally secure is a skill. Not everyone today has it.
"Sticks and stones, sister. Here, have a Valium." - Patti LuPone, a Memoir